War: Jehoshaphat's appeal to God and the answer

Nevertheless, when he had returned to his house, the king sets
himself to bring back the people to the fear of Jehovah, and to cause
judgment and righteousness to be executed in Israel. But war
begins. He could no longer have the unmingled blessing of having to do
with God alone without trial. The intervention of the enemy was now
needful for his good, according to God's government, although in the
trial through which he passes he may have full blessing. His piety
was genuine; the trial proves it. He appeals to the relationship of
God with Abraham and to His promises to Solomon, when the latter had
built the house. Jehoshaphat understood also the relation in which
the enemy stood to Israel, looked at in connection with God's dealings
(chap. 20: 10, 11). God answers him, and the king encourages the
people by acknowledging the voice of the prophets, and by singing the
praises of God before the blessing came -- singing in faith that His
mercy endureth for ever. God abundantly granted his prayer. Israel,
whose enemies had slain each other, had only to carry away the spoil;
and God gave rest to the king, and his realm was quiet.

Still, if Jehoshaphat no longer united himself with the king of
Israel to make war, he joined him in a matter of commerce. But God put
a stop to his undertakings.